In the field of liquid propellant rockets, the name “pogo effect” has been given to the entering into resonance of a liquid propellant in a feed circuit of the rocket engine with mechanical oscillations of the rocket. Since the thrust of the rocket engine varies with the flow rate of propellant delivered by the feed circuit, such entry into resonance can give rise to oscillations that diverge rapidly, and thus to difficulties of guidance, and even to damage that can go as far as total loss of the payload or even of the vehicle. The term “pogo effect” does not come from an acronym but rather from pogo sticks, which are toys formed by a rod having a spring whose bounces reminded technicians of the violent longitudinal oscillations of rockets suffering from this effect. From the beginning of the development of liquid propellant rockets, it has therefore been very important to provide systems for correcting the pogo effect. The term “pogo effect corrector system” is used to designate any system suitable for completely eliminating pogo oscillations or for limiting them to an amplitude that is low enough to not cause guidance difficulties or damage to the vehicle.
Among pogo effect corrector systems, systems of the capacitive type are known in particular, e.g. as disclosed in French patent No. 2 975 440. In such a system, the tank of a hydraulic accumulator is arranged around the pipe of a line for feeding the rocket engine with liquid propellant (e.g. the line for feeding liquid oxygen (LOx)), and communicates with the feed pipe via communications orifices formed in its lower part. A constant flow of gas (e.g. helium (He)) is injected into the upper part of the tank so as to maintain a bubble of gas in the tank, and a dip tube connects the liquid-gas interface to the liquid propellant feed pipe.
In known capacitive corrector system architectures, the tank is centered, i.e. it is coaxial with the propellant feed pipe, and the communication orifices are distributed uniformly around the propellant feed pipe.
Those known architectures present drawbacks in terms of overall size. Indeed, in a rocket or any other space vehicle, it is desirable to limit the size of the liquid propellant feed system that includes the corrector system, in particular in the interest of performance at liftoff.
For that purpose, it has been proposed to integrate the capacitive corrector system in a bend in the liquid propellant feed pipe. Such integration is described, by way of example, in the article “Design analysis of the Ares I POGO Accumulator”, Luke A. Swanson et al., 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Aug. 2-5, 2009, and it is shown diagrammatically in FIG. 1.
The known capacitive corrector system 100 comprises a feed pipe part 101 and a hydraulic accumulator comprising a tank 102. The feed pipe part 101 is bent, and is configured to be connected upstream to an upstream liquid propellant feed pipe 103 and downstream to a downstream liquid propellant feed pipe 104. The flow direction E of the liquid propellant is shown by an arrow in FIG. 1. The tank 102 is centered around the feed pipe part 101. The assembly between the feed pipe part 101 and the feed pipe 103 is carried out by means of a flange and bolts.
In that architecture, since it is necessary to conserve a certain amount of space for passing the bolts, the flange cannot be arranged immediately upstream from the tank 102 (position 105A in FIG. 1). On the contrary, in order to leave the space needed for passing the bolts during assembly, it is essential to make provision in the feed pipe part 101 for a rectilinear segment 101A upstream from the tank 102, and to place its flange at the upstream end of this rectilinear segment (position 105B of the flange in FIG. 1). The presence of the rectilinear segment 101A partly cancels out the space-saving achieved by incorporating the capacitive corrector system 100 in a bend.
Furthermore, since the tank 102 remains centered around the feed pipe part 101, so that the bubble of gas and the communication orifices are distributed uniformly around the feed pipe as explained above, the capacitive corrector system 100 cannot be used in a small space (e.g. when the height available under the bend is small), or on a bend having a radius of curvature that is small.
Furthermore, in practice, such a capacitive corrector system is entirely welded to the feed pipe, which presents drawbacks, in particular the drawback of being neither modular, nor capable of being disassembled, and thus not making it easy to change the configuration of the communication orifices, should that be found to be necessary.